Casting flask with improved heat transfer characteristics

ABSTRACT

A resurfacing for a worn interior wall of a cope or drag of a metal foundry flask includes a layer of thermal conducting substance between the outer surface of the liner plate and the inner wall surface of the flask.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to casting flasks and more particularly toa resurfacing for a worn interior wall of a cope or drag of a metalfoundry casting flask.

[0003]2. Description of Related Art

[0004] A typical foundry metal casting flask is formed of an upper copeand a lower drag which are aligned, one above the other, and filled withcasting sand within which a casting cavity is formed. Typically, dragand cope inside vertical walls are smooth and flat. In some cases, thecope walls may be flat, and in other cases, they may be provided withhorizontal grooves or lines for better retaining the casting sand whenthe cope is separated from the drag for the removal of the castingpattern.

[0005] In an automatic (flask-less) sand mold making machine, a singleflask may be repeatedly used to rapidly form sand molds. When each sandmold is completed, the cope and drag are separated from the cake or thesand mold which is then removed on a conveyor to a place where moltenmetal is poured into the flask-less sand mold. Alternatively, in someoperations, the flask remains with the sand mold until after the metalis cast and solidified. Then, the flask and sand mold are separated sothat the flask may be reused. In that case, numerous flasks are used.Throughout this process, there is considerable wear and tear on theinterior wall surfaces of the flask. Thus, the interior wall surfacebecomes rough, scratched, eroded or otherwise damaged by the abradingaction of the sand. Once the interior wall of the flask is roughened ordamaged, it becomes necessary to either replace the flask with a newone, or alternatively to rework the face to smooth and bring it back toits original finish. Either replacing the flask or refinishing the flaskwalls is relatively expensive and time consuming, requires stockingadditional flasks, and may result in considerable downtime in the caseof refinishing the flask walls in a automatic mold forming machine whichuses a single flask for making flask-less molds.

[0006] In the present practice, when the interior walls of a flask copeor drag become damaged or worn, the interior wall surfaces are repairedby covering them with stainless steel liner plates. The liner plates areformed of flat, stainless steel metal having outer faces forface-to-face engagement with the inner surfaces of the flask walls andinner faces that provide resurfaces, forming the inner faces of theflask.

[0007] The liner plates are bolted to the flask walls so that they maybe applied and removed for replacement when desired. Before applying thefirst liner plates, the worn inner wall surfaces of the flask may beground relatively level and flat to form a support base for the linerplates. Subsequent liner plate replacement ordinarily does not requireleveling the flask wall surfaces. In order to bolt the liners to thewalls, a large number of boltholes are formed in each of the liners.These boltholes are provided with deep countersinks at their inner facesso that bolts may be positioned within the holes with their bolt headsdeeply inset within the plates. That is, the bolt heads are spaced at adistance beneath the plane of the inner face of the liner plate.

[0008] Next, molten weld material is applied to the countersink openingsby using a conventional welding process to weld the bolts in place.Excess weld metal, which forms a bump over the countersink openings, isground flat. Thus, the inner face of each of the plates is smooth, andthe exposed surfaces of the welds are co-planar with the surfaces of theinner face. The liner plates are applied against the respective flaskwall surfaces with their welded-in-place bolts extending through thebolt receiving holes that are pre-drilled in the flask walls. Nuts areapplied to the ends of the bolts for fastening the liner plates to thewalls. Thus, the liner plates are rigid, but removably fastened withinthe flask walls to provide a replaceable surface.

[0009] A problem in replacing these work faces of cope and drag moldswith the stainless steel liners is a reduction in heat transfer capacityfrom an outside heat source to the sand mold or cable inside the copeand drag of the mold. Another problem encountered in the prior art isthat a small air gap that is inevitably formed between the liner and theinterior surface of the exterior wall of the flask. This air gappresents a substantial barrier to the transfer of heat to the liner andthence to the casting sand inside the cope and drag molds, requiring theapplication of more heat to the exterior of the flask, either byincreasing the level of applied heat or applying heat for a longerperiod of time.

SUMMARY OF INVENTION

[0010] An object of this invention is to provide a means for repeatedlyresurfacing the interior wall surfaces of a conventional cope or drag ofa flask used in a foundry for sand casting while maximizing heattransfer capability of the flask walls.

[0011] In accordance with one aspect of the invention, the problems ofthe prior art are alleviated by spreading a layer of a thermalconducting substance between the wall liners and the inside surfacewalls of the flask. Advantageously, the thermal conducting substancesubstantially eliminates any air gap between liner and the walls of theflask and aids in the transfer of heat through the flask walls to thesand mold.

[0012] In accordance with another aspect of the invention, the thermalconducting substance is a thermal conducting cement. In one particularembodiment of the invention, the thermal conducting cement is acommercially available, non-hardening product that allows for easyremoval of the worn plates.

[0013] Advantageously, the layer of thermal conducting cementsubstantially eliminates the air gap between the liners and the interiorwall surface of the flask and improves heat transfer from the exteriorof the wall to the interior of the flask.

BRIEF DESCRIPTION OF DRAWINGS

[0014] The invention will now be described with reference to thedrawings wherein:

[0015]FIG. 1 is a perspective view of a flask incorporating theprinciples of the invention;

[0016]FIG. 2 is a cross-sectional view along line 2-2 of the flask ofFIG. 1;

[0017]FIG. 3 is an enlarged, cross-sectional view along the line 3-3 ofFIG. 1;

[0018]FIG. 4 is a cross-sectional, exploded view of the wall of theflask in FIG. 1.

DETAILED DESCRIPTION

[0019] The cope 11 and drag 12 of a typical flask 10 as depicted in FIG.1 are box-like in shape and have opposite end walls and opposite sidewalls 13, 14, 16 and 17 which are interconnected by corner wall strips15, 18, 19 and 20. Some conventional flasks are rectangular inconfiguration, that is, with sharp corners, and other conventionalflasks may have angled corners. Step one to refurbishing a worn flask isto refinish the interior wall surfaces of the flask to form a smoothsurface. Next, a liner plate 30 is provided for each of the majorinterior walls of the flask. The liner plate is preferably formed of aflat, relatively thin, high quality low carbon steel liner plateprovided with a chrome plating, preferably on both sides of the linerplate. An outer face of the plate is arranged for face-to-face contactagainst the flask wall interior face. The liner plate has an outer face31 arranged for face-to-face contact against the flask wall interiorface 29, and inner face 32 against which the sand is compacted. Theliner is preferably sized to completely cover the interior surface ofthe flask wall. A layer of the thermal conducting cement 28 is spread onthe interior surfaces of side walls 13, 14, 16 and 17, and preferablyalso on the interior side walls of the corner wall strips 15, 18, 19 and20. One such thermal conducting cement is “TRACIT,” a well-known andcommercially available substance made by Chemax Corporation located inNew Castle, Del. The thermal conducting cement is preferably anon-hardening product cement to facilitate removal of the liner plateswhen the liner became worn.

[0020] The low carbon steel chrome liner plates 30 are secured to theflask wall, in a standard fashion, by means of suitable bolts 39extending through boltholes 37. Each bolthole is formed with a conicalcountersink 36 at the liner interface as depicted in FIG. 3 and the head40 of each bolt is closely fitted within the countersink of itsrespective bolthole. The countersink is relatively deep so that the bolthead is depressed or spaced beneath a plane defining the inner face 32of the plate 30. After the bolts 39 have been fully inserted in theliner plate 30, the space left in the countersink between the bolt headand the outer surface of the plate 30 is filled with a deposit of weldmetal. When the weld metal solidifies, it not only welds the bolt inplace and fills the space, but it also leaves an inwardly arranged bumpor roughness. That bump is ground down, as for example, by use of arotary surface grinder, until its exposed surface 45 is co-planar withthe inner face 32 of the plate.

[0021] Several tests were conducted to determine the effectiveness ofthe layer 28 of the thermal conducting cements the amount of energygoing into the flask, as well as the amount of energy coming out. Energygoing into the flask was determined by placing a first temperature gaugeon an outside surface of the flask at a specified distance away from theelectric heater. A second temperature gauge was placed on the inside ofthe flask directly opposite from the first temperature gauge to measureenergy transmitted through the flask wall. For all of the testsconducted, the same heater was used. This insured that the identicalamount of heat was going into the flask tested. All of the tests wereperformed in the same room, with all environmental variables being heldconstant from test to test. Each flask was allowed to reach a steadystate condition (room temperature) before the test was performed on it.All flask surfaces were cleaned of any foreign materials before testing.The following is the procedure for one test:

[0022] 1. With the heater and temperature gauges in place and the heaterturned off, the inside and outside temperatures are recorded. Since theflasks are all at steady state, both temperatures are the same.

[0023] 2. The electric heater is turned on and allowed to heat up. Thetime that the electric heater is turned on is recorded.

[0024] 3. Five minutes after the electric heater is turned on, both theinside of the flask and the outside of the flask temperatures arerecorded. The elapsed time is also recorded.

[0025] 4. The inside and the outside flask temperatures are againrecorded at various times after the heater has been turned on.

[0026] Table No. 1 shows the results of tests conducted on a rebuiltflask where no thermal conducting cement was used. Table No. 2 shows theresults of tests conducted on a rebuilt flask where a layer thermalconducting cement 28 was applied between the flask wall 14 and the plate30. TABLE 1 REBUILT FLASK No Thermal Conducting Cement Used OutsideFlask Inside Flask Elapsed Time Temperature Temperature Outside Temp (−)Time (minutes) (° F.) (° F.) Inside Temp. 1:40 0 70 70 0 1:45 5 72 71 11:50 10 80 80 0 2:00 20 102 92 10 2:15 35 110 108 2 2:35 55 110 111 −1

[0027] TABLE 2 REBUILT FLASK Thermal Conducting Cement Used BetweenLiner and Flask Wall Outside Flask Inside Flask Elapsed Time TemperatureTemperature Outside Temp (−) Time (minutes) (° F.) (° F.) Inside Temp.10:40 0 76 76 0 10:45 5 81 88 −7 10:50 10 96 104 −8 11:00 20 106 110 −411:10 30 120 124 −4 11:35 55 134 132 2

Having fully described an operative embodiment of this invention, what is claimed is:
 1. A casting flask comprising a plurality of outer walls each having an interior wall surface and an exterior wall surface, said flask further comprising: a liner plate mounted to said interior wall surface of at least one of said outer walls, said liner plate having an outer surface disposed adjacent said interior wall surface and an inner surface disposed opposite said outer surface; and a layer of a thermal conducting substance disposed between said outer surface of said liner plate and said inner wall surface.
 2. The casting flask in accordance with claim 1, wherein said thermal conducting substance is a substance known by the trade name of “TRACIT.”
 3. A method of relining an outer wall of a casting flask having an interior wall surface, said method comprising the steps of: applying a layer of a thermal conducting substance to said interior wall surface; and attaching a liner plate to said interior wall surface adjacent said layer of thermal conducting substance, whereby said thermal conducting substance is disposed between said liner plate and said interior wall surface.
 4. The method in accordance with claim 3, and further comprising the step of grinding said interior wall surface, to present a relative smooth interior wall surface, prior to said step of applying said layer of thermal conducting substance. 